Abstract:

Since the pre-fermentation of Bagongshan sufu has an important impact on its overall nutritional quality and
flavor and the exploration of its fermentation process with two common strains (Mucor racemosus or Rhizopus oryzae)
is of great significance for practical production. The conditions for pre-fermentation of either strain were optimized by
the combined use of one-factor-at-a-time method and response surface methodology. Fermentation time, temperature
and inoculum amount were selected as independent variables while protease activity was selected as response variable.
This study also compared the enzyme systems and amino acids produced by the two stains under optimized fermentation
conditions. Results showed that the optimal fermentation conditions of Mucor racemosus were found to be fermentation
for 60 h at 24 ℃ with an inoculum amount of 1.0 × 105 CFU/mL. Under these conditions, the activity of protease was
42.79 μg/mL. The optimal fermentation conditions of Rhizopus oryzae were determined as 50 h, 32 ℃ and 1.0 × 105 CFU/mL,
respectively. Under these conditions, the activity of protease was 33.51 μg/mL. Comparative investigations indicated that
the activity of protease in Mucor racemosus was higher than that in Rhizopus oryzae, while α-amylase, glucoamylase and
lipase from Mucor racemosus were lower than from Rhizopus oryzae. The content of total amino acids in sufu fermented by
Mucor racemosus was higher than that in sufu fermented by Rhizopus oryzae while there was no obvious difference in flavor
amino acids or hydrophobic amino acids. Both Mucor racemosus and Rhizopus oryzae had their own advantages for the
pre-fermentation of Bagongshan sufu, which may lay a theoretical foundation for synergistic fermentation.

Key words: sufu, pre-fermentation, Mucor racemosus, Rhizopus oryzae, amino acid